An air battery using oxygen as a cathode active material has advantages of high energy density, enabling reduction in size and weight, etc. Accordingly, it has received attention as a higher-energy density battery than lithium secondary batteries that are widely used now. Examples of air batteries include metal-air batteries such as lithium-air, magnesium-air, zinc-air and aluminum-air batteries.
A metal-air battery enables charge and discharge by oxidation-reduction reaction of oxygen at the air cathode (cathode) and oxidation-reduction reaction of an anode active material at the anode. A general metal-air battery comprises, for example, an air cathode containing an electroconductive material and a binder, an air cathode current collector for collecting current from the air cathode, an anode containing an anode active material (metal, alloy, etc.), an anode current collector for collecting current from the anode, and an electrolyte present between the air cathode and the anode.
For example, in a metal-air battery (secondary battery) in which the migrating ions are monovalent metal ions, it is thought that the following charge and discharge reactions proceed. In the following formulae, M means a metal species.
(Upon Discharge)M→M++e−  Anode2M++O2+2e−→M2O2 4M++O2+4e−→2M2O  Air cathode
(Upon Charge)M++e−→M  AnodeM2O2→2M+O2+2e−2M2O→4M++O2+4e−  Air cathode
The above charge and discharge reactions occur in the case where the electrolyte is a non-aqueous liquid electrolyte or solid electrolyte, and the metal oxide produced at the air cathode upon discharge is deposited at the air cathode. On the other hand, in the case where the electrolyte is an aqueous liquid electrolyte, it is thought that the following charge and discharge reactions proceed. Upon discharge, in the liquid electrolyte, the dissolved metal ion (M+) reacts with the hydroxide ion (OH−) to produce a water-soluble metal hydroxide.
(Upon Discharge)M→M++e−  AnodeO2+2H2O+4e−→4OH−  Air cathode
(Upon Charge)M++e−→M  Anode4OH−→O2+2H2O+4e−  Air cathode
To promote the electrode reaction at the air cathode upon discharge and/or charge (oxidation-reduction reaction of oxygen) and thus to increase the battery characteristics of an air battery, a catalyst is added to the air cathode (for example, Patent Literature 1).
In particular, a lithium-air secondary battery is disclosed in Patent Literature 1, comprising: a cathode comprising a gas diffusion type oxygen electrode mainly composed of carbon; an anode comprising a lithium metal or a material being able to absorb and release lithium ions; and a non-aqueous electrolyte medium present between the cathode and the anode, wherein Fe-based oxide La1-xAxFe1-yByO3 (A: alkaline earth metal, 0≦x<1.0, B: transition metal, 0≦y<1.0) having a perovskite structure, is contained as an electrode catalyst in the cathode.